1. Field of the Invention
The present invention relates to a regulating device for a hydrostatic positive displacement unit, such as an axial piston machine employing the swash plate principle, with a control valve which pressurizes a regulating piston which determines the stroke volume or the displacement volume of the positive displacement unit.
2. Background Information
During the operation of hydrostatic positive displacement units, it has been found to be advantageous if the stroke volume or the absorption volume can be adjusted by changing the inclination of a tilting yoke, such as a swash plate, to correspond to different operating conditions. The prior art discloses mechanical or hydraulic regulating devices which can be actuated and controlled mechanically, hydraulically or electrically.
Hydraulic regulating devices have at least one regulating piston which is engaged with a tilting yoke, such as a swash plate, and the tilting angle of this body determines the stroke volume or the absorption volume of the positive displacement unit. The regulating body is pressurized by a control valve which generates a control pressure.
To improve the control and regulation of the regulating device, the prior art discloses that the regulating device can be actuated electrically. For this purpose, the prior art discloses systems which have a proportional valve which is actuated by a proportional magnet.
In such a regulating device, the proportional magnet converts an electrical control signal into a magnetic force which deflects a pressure relief valve against the force of a spring. The pressure relief valve is connected to a pressure source and generates a control pressure as a function of the deflection. The control pressure deflects a spring-loaded control piston, the travel of which is transmitted by a mechanical intermediate element to a control valve which is located on the tilting yoke. The control valve is thus piloted by the control pressure and is actuated by the mechanical intermediate element. From a supply pressure, the control valve generates a control pressure which is used to pressurize the regulating piston of the hydraulic regulating unit, thereby regulating the tilting yoke. The control travel is transmitted back to the control valve by a mechanical linkage, wherein--as a function of the distance traveled by the control piston--the control valve is once again closed when the tilting yoke reaches the desired inclination.
To produce the tilting angle on the tilting yoke of the positive displacement unit by the electrical control signal, these systems require five conversions in the signal chain. Each of these conversions is subject to deviations within the specified tolerances and each requires additional components. Friction also occurs in the spring-loaded components and is reflected these systems in the form of hysteresis. The fact that the control valve is located directly on the tilting yoke also increases the cost and complexity of the supply pressure line and of the lines which lead to the regulating piston.